1. Field of the Invention
The present invention generally relates to a marine obstacle avoidance system and, more particularly, to a method of alerting a helmsman of a marine vehicle to the danger of maritime collision with floating and/or submerged obstacles.
2. Description of the Prior Art
The danger of maritime collisions during daylight or nighttime conditions is well documented. It is known to transmit acoustic signals by an underwater sound transmitter and to thereupon detect the reflected acoustic echo signal (i.e. sonar) for the purpose of finding underwater objects. It is also known to transmit microwave signals from an abovewater microwave transmitter and to thereupon detect the reflected microwave echo signal (i.e. radar) for the purpose of finding abovewater objects. Other than by direct visual sighting, there is no known way to detect objects floating at, slightly below or slightly above the water's surface.
As shown in U.S. Pat. Nos. 2,732,539, 3,203,305; 2,972,924; and Great Britain No. 1,237,480, optically-based collision avoidance systems have never been used on boats heretofore, and no previous shipboard system is known to me which is operative for detecting both floating and submerged objects, either simultaneously or separately.